They actually aren't secret overlords in the series. Instead, they made strategic alliances with certain humans: police chiefs, coroners, etc.- in order to maintain the secret if their existence. They work with those humans and with each other because to do otherwise invites destruction. They're more like parasites than overlords.
Part of the reason it works is that vampires in this setting are not perpetually bloodlust driven killers who need human blood to live. Instead, their relationship with blood is more like junkie and drug.
The decadent ones fall into a couple of classes- the truly mad, the would-be overlords (who want what the vampires of fiction have), and the numb jaded ones. But they're more diverse than that. The show's lead was once l
One of their leaders...until he gave up human blood, making him outcast.